Production of electrodes for alkaline storage batteries wherein active material is at least partially formed from the metals in said grid



United States Patent 9 Claims. (61. 136-6) ABSTRACT OF THE DISCLOSURE Aprocess for producing electrodes for alkaline storage batteries inwhichthe metal of the grid itself is used in the formation of the activematerial. A solution containing a weak acid and a metal salt having anoxidizing anion is placed in contact with the grid. This activates thegrid whereupon the grid is treated with an aqueous alkali metalhydroxide solution. The process provides a simple means for producingelectrodes of this type.

This application is a continuation of application Ser. No. 281,361,filed May 17, 1963, now abandoned.

This invention relates to a process for the production of electrodes foralkaline storage batteries, especially to electrodes consisting ofelectrochemically inactive grids the pores of which contain the activematerial.

It is known that efficient positive electrodes for alkaline storagebatteries can be prepared by introducing nickel hydroxide or mixtures ofnickel and cobalt hydroxides as an active composition into the pores ofporous electrode grids, made for example of metallic nickel. Accordingto the process of British patent specification No. 331,540 this may beeffected by impregnating the electrode grid with a solution of a nickelsalt, for example concentrated nickel nitrate solution, if desireddrying the impregnated electrode grid and then precipitating the nickelsalt as nickel hydroxide in the pores by treatment with an alkalinesolution, the electrode then being washed and dried. The nickel nitratesolution introduced into the pores by impregnation may also exert anoxidizing action on the skeleton so that in this way part of the activecomposition is formed from the electrode grid itself. In this process itis necessary in every case to repeat the said operations, i.e.impregnation, precipitation, washing and drying, several times in orderto achieve an adequate capacity for the electrodes. According to theprocess described in British patent specification No. 487,607 nickelhydroxide is precipitated from the nickel nitrate solution in the poresof the electrode grid by cathodic polarization. In this process also,however, repetition of the impregnation and polarization processes isindispensable for the achievement of adequate capacity.

It is an object of the present invention to provide a simpler method forthe production of the said type electrodes. It is a further object ofthe present invention to provide a process for the production of thesaid electrodes in which the metal of the electrode grid itself can beutilized for the formation of the active material, i.e. it isunnecessary in the case of the positive electrode to supply nickelnitrate solution from outside. These and other objects and advantages ofthe invention are achieved when a solution containing at least one weakacid and a metal salt having an oxidizing anion is allowed to act on anat least partly metallic electrode grid which is inactive with respectto the electrolyte and the electrode grid is then treated with anaqueous solution of an alkali metal hydroxide.

In addition to nitrates, persulfates are particularly suitable as anionshaving an oxidizing action.

With the activation of the electrode grid according to the presentinvention, a capacity which can only be achieved by prior art methods byrepeating the process several times, is achieved with only a singleimpregnation followed by treatment with an aqueous solution of an alkalimetal hydroxide. When using metal nitrates for the impregnation of theelectrode grid, less aqueous alkali metal hydroxide solution is used inthe subsequent alkaline treatment than in the prior art methods. Thetreatment according to the invention may be repeated to increase thecapacity, if desired after a short rinsing of the electrode with water,and in contrast to the prior art methods an alkaline treatment of theelectrode grid after the first impregnation may if desired be omitted.

The solution used for the impregnation of the electrode isadvantageously prepared by dissolving a metal nitrate, for examplenickel nitrate, in an aqueous solution of a weak acid, for exampleacetic acid, propionic acid, citric acid or derivatives of the saidacids, e.g. glycocoll. Salts of the weak acid used may also be added tothe solution. The concentration of the acid used may be varied withinwide limits. An activating influence is noticeable even with a 10%aqueous solution of the acid. It is ad vantageous to use an aqueoussolution which contains the acid in an amount of 15 to 50% by weight.

The favorable effect of a Weak acid on the activation of an electrodegrid is not limited to nickel nitrate but extends also to othernitrates, for example cobalt nitrate. Even solutions of nitrates whichby themselves have only quite an insignificant activating effect orwhich behave entirely indifferently to porous nickel grids, such as thenitrates of the alkali metals or other strongly basic metals andmixtures of these nitrates with nickel or cobalt salts, e.g. sulfates,have a strong activating effect after a weak acid has been addedthereto. When the activating solution contains metal salts which forminsoluble hydroxides in alkaline solutions, in addition to nickel salts,the hydroxides of these metals are also precipitated in the pores bytreatment of the electrodes.

Electrode grids impregnated according to this invention are exposed,prior to treatment with aqueous alkali hydroxide solution, to the actionof the impregnating solution for a certain period which dependssubstantially on the desired capacity and the temperature at which thetreatment is carried out. It is advantageous to use elevatedtemperatures, for example temperatures of more than 50 C., because thisaccelerates the formation of the active composition. It is of advantageto work at temperatures of about 70 to C. In general it is sufiicient tocarry out the treatment for one to two hours but this period may beshortened or lengthened depending on the conditions chosen and thecapacity required. It is further advantageous to perform the activationof the grid which has been impregnated with the acid solution in anatmosphere saturated with water vapor.

By the process according to this invention it is possible not only toproduce the active composition by activation of the electrode griditself, but at the same time to introduce a considerable proportion ofthe active composition into the electrode grid from outside, for exampleby the use of nickel nitrate solutions. This is important becauseparallel with the formation of the active composition from the electrodegrid, weakening of the mechanical strength of the grid takes place.Depending on the use to which the electrodes prepared are to be put itis possible by variation of the concentrations of the solution used andof their period of action on the grid, either to form more activecomposition from the nitrate solution introduced into the grid fromoutside, so that more mechanically stable grids are obtained, or toincrease the proportion of active composition which is formed byactivation of the electrode grid, in which case a decrease in themechanical stability of the electrodes must be taken into account.

The following example will further illustrate the invention.

Example A porous nickel sintered plate weighing 4.26 g. and having thedimensions 76 x 28 x 0.90 mm., which is reinforced by a thin perforatedsheet of nickel embedded therein during sintering, is immersed in asolution containing 2 parts of crystallized nickel nitrate in 1 part of30% by weight acetic acid and then treated for about two hours at atemperature of about 80 C. in an atmosphere saturated with water vapor.Then the plate is placed for half an hour in hot 20% caustic potashsolution and thereafter rinsed thoroughly with water and dried. Afterrepeating this treatment, the nickel sintered plate has increased inweight by 1.4 g. Of this increase in weight, 0.65 g. is accounted for bythe nickel hydroxide formed from the nickel nitrate introduced fromoutside with the activating solution and 0.75 g. is due to the formationof nickel hydroxide by oxidation of the nickel sintered grid itself.When used as an electrode, the plate has a capacity of 0.75 amperehours, this being about the value to be expected theoretically.

What I claim is:

1. A process for producing electrodes for alkaline storage batteriescomprising the steps of treating an at least partly metallic porouselectrode grid which is inactive to electrolytes with an aqueoussolution consisting essentially of at least one weak acid dissolved inwater, said acid being a member selected from the group consisting ofacetic acid, propionic acid, citric acid and glycocoll and a metal salthaving an oxidizing anion, and subsequently treating said grid with anaqueous solution of an alkali metal hydroxide whereby electrochemicallyactive material consisting of oxidic compounds of the metals containedin said grid are formed within the pores of said grid, said activematerial being at least partially formed from the metals contained insaid grid.

2. A process as in claim 1 wherein the porous electrode grid is made upat least partly of nickel.

3. A process as in claim 2 wherein the metal salt is anitrate.

4. A process as in claim 2 wherein the metal salt is nickel nitrate.

5. A process as in claim 2 wherein the metal salt is cobalt nitrate.

6. A process as in claim 2 carried out at a temperature of more than C.

7. A process according to claim 2 wherein the treatment of the grid withsaid aqueous solution consisting essentially of at least one weak aciddissolved in water and a metal salt having an oxidizing anion is carriedout in an atmosphere saturated with water vapor.

8. A process as in claim 2 wherein the aqueous solution is prepared byadding a salt of said weak acid and a metal salt having an oxidizinganion to water.

9. A process as in claim 2 wherein said solution contains said aqueousweak acid in the amount of 15 to 50% by weight.

References Cited UNITED STATES PATENTS 2,880,257 3/1959 Murphy et al.136-29 3,041,388 6/1962 Fukuda et al. 136-24 3,203,879 8/ 1965 Mueller204-56 3,269,864 8/1966 Ackermann et al. 136-78 FOREIGN PATENTS 232,1933/1959 Barak et al.

0 WINSTON A. DOUGLAS, Primary Examiner.

A. SKAPARS, Assistant Examiner.

Patent No.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,356,534 DecemberS, 1967 Karl Ackermann It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected asshown below:

Column 4, line 26, after "said" insert aqueous Signed and sealed this16th day of December 1969.

(SEAL) Attest:

Edward M. Fletcher, In

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR.

1. A PROCESS FOR PRODUCING ELECTRODES FOR ALKALINE STORAGE BATTERIES COMPRISING THE STEPS OF TREATING AN AT LEAST PARTLY METALLIC POROUS ELECTRODE GRID WHICH IS INACTIVE TO ELECTROLYTES WITH AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF AT LEAST ONE WEAK ACID DISSOLVED IN WATER, SAID AID BEING A MEMBER SELECTED FROM THE GROUP CONSISTING OF ACETIC ACID, PROPIONIC ACID, CITRIC ACID AND GLYCOCOLL AND A METAL SALT HAVING AN OXIDIZING ANION, AND SUBSEQUENTLY TREATING SAID GRID WITH AN AQUEOUS SOLUTION OF AN ALKALI METAL HYDROXIDE WHEREBY ELECTROCHEMICALLY ACTIVE MATERIAL CONSISTING OF OXIDIC COMPOUNDS OF THE METALS CONTAINED IN SAID GRID ARE FORMED WITHIN THE PORES OF SAID GRID, SAID ACTIVE MATERIAL BEING AT LEAST PARTIALLY OFRMED FROM THE METALS CONTAINED IN SAID GRID. 